It's not just developing countries that are cheaper than the US, it seems. In the UK my 100 minutes, 100 text, unlimited data contract costs me £15 a month (~$22) and came with a free smartphone (a Samsung Galaxy Apollo - a mid end Android job).

Its not the cost of the HW.
Heck, i still dont have a cell phone, dumb or smart.
600+$ / yr is ridiculous!
I refuse to have two phones, plus
when I m visiting people, its rude to be interrupted any way.
Yes, I m a luddite.
I dont do cable TV either.
Broadcast is where its at.

3-4 years ago, one of my colleague actually bought $100 PC for interest. We were surprised how useless it was!
Some people make things cheap will open up a huge market opportunity, but the product must have practical usefulness. Q-core cortexA7 + 1080p video support sounds reasonable, but if it comes with cheap low-resolution LCD plus terrible precision touch screen, the product will be much more useless than purpose-built feature phone.

I've been listening for years about laptops for $100 (for Africa, Asia... etc...), then for similarly cheap net-books, then phones, and now for some time the same fairy-tales for tablets.
During last 15 years I've probably heard minimum 100 times someone announced that cheap ___put_here_whatever_popular_computing_device__ is knocking at the door.
And it never happened.
It won't happen this time either.

Always wondered why US phone contracts are so expensive. I mean I can get a 24 month contract with monthly 4GB LTE data + 300 min voice calls +~1000SMS for 45US$ in singapore along with a subsidized(around 300-400$ less) phone. IIRC similar contracts are 70-80$ in the US

Yes you're right. I pay about $7 a year in mobile phone bills in Thailand. For this price I obviously don't use data plan, and connect via Wi-Fi instead.
I'm always surprised to read $100 tablets and smartphones are the future, since in 2012 you could get a $60 7" android tablet with Cortex A8 or Cortex A9 processor, and for $75 you could get Android smartphones based on some of the Mediatek processors.